1. Field of the Art
This invention relates to method and apparatus for coating a resin, and more particularly to method and apparatus for coating a surface of a substrate plate with a thin film of a curable resin or plastic suitable for use in imprinting a pattern of infinitesimally minute dents and projections.
2. Prior Art
In the so-called nano-imprinting, a rectilinear or circular pattern of infinitesimally minute dents and projections is transferred to a surface of a substrate plate of an arbitrary shape by a hot embossing, molding or stamping process. In any case, a curable resin film is coated on a surface of a substrate plate in a preparatory stage. In the case of a stamping process, a photo-setting synthetic resin is coated on a substrate plate, followed by impression of a mold against the coated resin film to transfer a pattern of minute dents and projections to the coated plastic film from a transfer surface of the mold. While the mold is in an impressed state, the resin film is irradiated with light rays for setting the resin. The substrate plate which comes out upon separation from the mold has a pattern of minute dents and projections transferred on its surface.
With a substrate plate of a circular or annular shape, it has been the general practice to coat the substrate plate with a resist film by the use of a high speed spin machine as described in Japanese Laid-Open Patent Application H6-333807, for example. Namely, in this case, a work in the form of a circular glass plate is put on a turn table, and, while the turn table is rotated at high speed, a resist liquid is dripped on a work surface from a resist liquid feed nozzle which is moved radially from the center to the outer periphery of the turn table. Since the work is rotated along with the turn table, the resist liquid is fed onto the work surface in a spiral shape and urged to flow in radially outward directions under the influence of centrifugal force to form a resist film over the entire surface of the work.
As described above, a resist liquid is applied by high speed spin coating in Japanese Laid-Open Patent Application H6-333807. In the case of the high speed spin coating, a resist liquid is spread with the aid of centrifugal force. In that case, however, there is a difference in circumferential speed between inner and outer peripheral areas, so that the resist liquid is subjected to greater centrifugal force in outer peripheral portions than in inner peripheral portions, and as a result a coated resist film has different thicknesses in inner and outer peripheral portions of the substrate plate. Besides, in the case of the high speed spin coating as in Japanese Laid-Open Patent Application H6-333807 mentioned above, there is a limit to reduction of film thickness. That is to say, the method of Japanese Laid-Open Patent Application H6-333807 can be suitably applied to a process for coating a resist film on a master of an optical disc, but cannot be applied to a process for coating an extremely thin resin film uniformly on a work surface.
For example, to cope with the trends toward larger storage capacities and higher densities of semiconductor integrated circuits, magnetic discs and optical discs, there have been developed and put in use nano-structure devices having a pattern of infinitesimally minute dents and projections on a surface of a substrate plate. As described in Japanese Laid-Open Patent Application H6-333807 mentioned above, the hot embossing technology which is generally applied in the production of an optical disc master has a limit in the size of minute dents and projections to be formed on a substrate plate. Beside the hot embossing, neither the molding process nor the stamping process cannot be applied to nano-imprinting in case of a pattern involving dents and projections smaller than several tens nanometers. This is because, in the case of nano-imprinting, it is required to coat an extremely thin resin film uniformly on a surface of a substrate plate and with extremely high accuracy. At least from the standpoint of mass production, the high sped spin coating is unsuitable for application to a process for manufacturing resin-coated substrate plates which are strictly controlled in thickness of resin film.